1. Field of the Invention
The present invention relates to a technology for crystallizing a semiconductor by irradiation with laser light. Further, the present invention relates to a method for forming a semiconductor device using a semiconductor film crystallized by being irradiated with laser light.
2. Description of the Related Art
Technologies for crystallizing an amorphous silicon film by irradiation with laser light is one of the important technologies in order to form a semiconductor integrated circuit using thin film transistors (TFTs) without the use of a silicon wafer.
For example, there is a known technology: a film which is heated by absorbing laser light is formed on an amorphous silicon film and heat generated in the film is utilized, thereby forming crystalline silicon with a large grain diameter. For example, Reference 1 (Japanese Published Patent Application No. 2003-178979) describes: a blocking layer, a semiconductor film shaped into a predetermined form, a barrier film, and a thermal insulating film formed of amorphous silicon are staked in this order over a substrate, and irradiation with laser light from a continuous wave laser is performed from the substrate side, whereby a semiconductor region is melted and crystallized; and the propagation direction of heat in the semiconductor film is controlled with the thermal insulating film; accordingly, the diameter of crystal grains can be increased (refer to the paragraphs [0045], [0057], and the like in Reference 1).
Further, Reference 2 (Yuta SUGAWARA and 5 others, “crystallization of a Si thin film with a two-layer structure by 22a-W-8 solid green laser anneal,” preliminary drafts for the 53rd spring meeting of the Japan Society of Applied Physics and Related Societies in 2006, No. 2, p. 888 (March, 2006)) reports that SiN, SiO2, first a-Si, SiO2, and second a-Si are stacked over quartz glass, and irradiation with solid green laser light with a wavelength of 532 nm is performed, so that the first a-Si is crystallized to be microcrystalline Si, and the second a-Si is crystallized to be polycrystalline Si with a grain diameter of about 1 μm. According to the report of Reference 2, it is considered that the first a-Si effectively functions as a heat source in this crystallization.
Reference 3 (Japanese Published Patent Application No. 2003-168646) describes: an amorphous silicon film and a molybdenum film are stacked in this order over a substrate, and the molybdenum film is irradiated with laser light from a continuous wave YAG laser, whereby the molybdenum film is heated and the amorphous silicon is melted by heat of the molybdenum film and thus crystallized.
Reference 4 (Japanese Published Patent Application No. H4-212410) describes: amorphous silicon is crystallized by irradiation with incoherent light such as lamp light instead of laser light. In Reference 4, an amorphous silicon film, an insulating film, and a light absorption layer are stacked in this order over a substrate, and irradiation with lamp light is performed to heat the light absorption layer, so that the amorphous silicon film is crystallized by heat conducted from the light absorption layer. For the light absorption layer, a metal such as tungsten or molybdenum, polycrystalline silicon, or amorphous silicon is used.
Further, Reference 5 (Masato MAKI and 3 others, “laser crystallization 2 of a silicon film using a 22a-W-9 diamond-like carbon light absorption layer,” preliminary drafts for the 53rd spring meeting of the Japan Society of Applied Physics and Related Societies in 2006, No. 2, p. 888 (March, 2006)) reports that a diamond-like carbon film is used for the light absorption layer, and an amorphous silicon film is crystallized by continuous wave Nd+:YAG laser light with a wavelength of 1064 nm.